During the use of optical modules, various problems are inevitable. When we connect the optical module to the optical module through fiber optics, there may be situations where the optical port light is not on, the optical port light is red, or an alarm or failure of the optical module occurs. So, where is the fault with the optical module? Is it a fault at the transmitting end or receiving end of the optical module? Is it an internal issue with the optical module itself? Is it due to improper external use that caused the malfunction? This article summarizes common faults of optical modules and provides corresponding solutions to help detect and troubleshoot faults in the use of optical modules.

Common internal faults and solutions of optical modules

In the daily use of optical modules, we may encounter internal faults such as poor optical power, poor eye diagram, poor receiver, poor working current, and program programming failures. When encountering the above faults, we can troubleshoot the optical module by inspecting its appearance to see if there is obvious damage, or by using some tools to compare it with a intact optical module.

The following content takes 1G SFP optical modules as an example to provide a detailed explanation of the causes of optical module failures, corresponding fault detection methods, and fault solutions.

Fault 1: Degradation of optical power performance of the optical module

The degradation of optical power performance in optical modules may lead to the following phenomena:

1. The bias current is within the normal range, and the optical power exceeds/falls below the control range;

2. No light on, BIAS value displayed as 0, or BIAS short circuit, with a large value displayed as 90mA~150mA;

3. During the debugging process, some lights are on, but the optical power remains unchanged;

If the first phenomenon mentioned above occurs in the optical module, it may be due to damage to the TOSA emission components of the optical module, poor soldering of TOSA PINs PD+, or mismatch between power and resistance and bias current. The corresponding solutions include: replacing the TOSA emission components of the optical module, re soldering and reinforcing TOSA PINs PD+, or adjusting power and resistance;

If the second phenomenon mentioned above occurs in the optical module, it may also be due to poor soldering of TOSA PINs PD+, or failure of the storage chip or damage to the magnetic beads on the LD -/LD+line. The corresponding solutions include: re soldering and reinforcing TOSA PINs PD+, replacing the storage chip on the optical module, and reconnecting the same type of magnetic beads on the LD -/LD+line;

If the third phenomenon mentioned above occurs in the optical module, it may also be due to damage to the TOSA emission components or poor soldering of TOSA PINs LD -. In this case, it is recommended to replace the TOSA emission components or re weld and reinforce the TOSA PINs PD+.

Fault 2: Poor optical module eye diagram

The poor eye diagram of optical modules generally includes several phenomena, such as poor extinction rate, scattered eye diagram, irregular pattern, or absence of eye diagram.

The reason for poor extinction rate is that the extinction ratio is too high or too low. In this case, the TOSA emission component should be replaced or the optical power resistance should be reduced/increased;

The causes of eye pattern scattering in the optical module include TOSA damage, poor performance of the driver chip, or mismatched signal impedance. In this case, the internal TOSA of the optical module should be replaced, the driver chip should be replaced, or the front-end matching resistance should be changed;

When there is an irregular pattern in the eye diagram of the optical module, it is necessary to modify the values of the pull-up/pull-down resistance and matching resistance;

When there is no eye pattern phenomenon in the detection of the optical module, it is due to TOSA damage or poor welding of the matching resistor at the front end. At this time, replace the damaged TOSA component or re weld and reinforce the matching resistor.

Fault 3: Poor performance of the optical module receiving end

The performance of the receiving end of the optical module is poor, mainly due to two phenomena: low sensitivity (or even no sensitivity at all), or alarm dysfunction.

There are many reasons that can cause low sensitivity or sensitivity failure in optical modules. Common ones include damage to ROSA components, poor contact between ROSA pins OUT+and OUT -, low extinction ratio of light sources, poor or missed soldering of magnetic beads, damage or poor performance of limiting amplifier chips. To address these reasons, solutions include replacing ROSA components in the optical module, re soldering and reinforcing ROSA, adjusting extinction ratio to 10+, and re pasting magnetic beads Replace the limiting amplifier;

When the optical module experiences alarm dysfunction, the main reason is that the ROSA component is damaged or the alarm resistance does not match. At this time, only the ROSA component needs to be replaced or the alarm resistance value needs to be changed.

Fault 4: Poor operating current performance of the optical module

There are three phenomena of poor operating current performance of optical modules:

1. The open circuit working current is less than 70mA;

The main reason for the above situation is that the MOS of the optical module is damaged, or the program has not been burned yet. At this time, only the MOS tube needs to be replaced or the program needs to be burned again.

2. The working current is greater than 300mA;

When the above situation occurs in the optical module, it is necessary to replace the components or observe whether there is poor soldering or SMT between the components.

3. Short circuit action current greater than 500mAV;

The main reasons for the above situation are TOSA/ROSA or internal short circuits in the chip, or the presence of tin in various components of PCBA, or short circuits in VCC and GND of PCBA. When encountering these situations, it is necessary to replace the damaged TOSA/ROSA or chip. If there is still tin in the PCBA components, the tin should be evenly separated. If the current caused by the short circuit of PCBA is too high, the only option is to scrap the PCBA, which cannot be repaired.

Fault 5: Programming failure of optical module program

There are three main phenomena of programming failure in optical modules:

1. The program cannot be burned;

The main reasons for the above phenomenon in the optical module are poor performance of the MOS transistor or chip placement, poor chip performance or patch preservation. In this case, it is necessary to replace, re paste the MOS or save the chip.

2. The program can be burned but does not have an ID;

The main reason for the above phenomenon in the optical module is that the storage chip components are damaged or missing, and in this case, it is necessary to re paste the same type of components.

3. Short circuit in module or casing;

The modules include TOSA, ROSA, and PCBA, among which only TOSA is metal and connected to the casing. If there is a short circuit in the module or casing of the optical module, the TOSA component needs to be replaced, and then the short circuit needs to be observed. If there is a short circuit, it means that the PCBA or TOSA is damaged. In this case, the TOSA needs to be replaced or the PCBA needs to be scrapped.

Common external faults and solutions of optical modules

In addition to internal faults of the optical module, the operation of the optical module during use may also cause external faults of the optical module, mainly manifested in the following four types:

1. The power light is not on;

This phenomenon is often a power failure, which requires checking the power cord or replacing the power supply.

2. The link light is not on;

Check if the fiber optic circuit is intact, if the connection between the equipment interface and the fiber optic jumper is loose, and if the fiber optic jumper is disconnected from the coupler;

Check if the fiber optic line loss is too large and if it exceeds the loss budget of the used transmitting/receiving pair;

Check if the optical interface is properly connected, whether the remote local TX and RX are connected, and whether the remote local RX and TX are connected;

Check if the fiber optic jumper is correct, ensure that the connector type matches the device interface (APC/UPC/PC), the fiber optic type (MMF/SMF) matches the device type, and the supported transmission length matches the link distance.

3. The circuit link light is not on;

Check if the network cable is a circuit breaker;

Check if the connection type matches (computers and other devices use crossover cables, switches, hubs and other devices use straight lines);

Check if the device transmission rate matches.

4. Severe network packets;

The power port of the transceiver does not match the network device interface or the transmission method of the two end device interfaces (half duplex/full duplex) does not match;

RJ-45 head distortion issue;

Fiber optic connection issues, misaligned fiber optic jumpers, or mismatched couplers and jumpers.

Optical Module Installation Guide

Avoiding internal failures of optical modules may not be easy, but through some installation guidelines for optical modules, we can reduce unnecessary failures that may be caused by external factors during the installation process.

Before installing the optical module, we need to conduct a careful inspection:

1. Check the conductive metal, a good transceiver module should look bright and tidy;

2. Check if the bundling buckle is intact;

3. Check the optical module port interface to ensure that there are no obvious issues inside;

4. Check if the plug of the jumper is damaged.

After completing the preliminary inspection and ensuring that there are no issues with the relevant equipment and modules, proceed with the installation of the optical module. How to install and connect optical modules? The following text will continue to explain the installation steps of the optical module.

Step 1: Remove the dust plug from the device slot where the optical module is to be installed; (Tip: If you are not ready to install the optical module immediately, do not remove the dust plug on the device slot, otherwise it will cause the device port to be contaminated)

Step 2: Insert the optical module horizontally into the device slot. If you hear a "click" sound, the optical module is correctly inserted;

Step 3: Remove the dust cap of the prepared fiber optic jumper and clean the fiber optic plug;

Step 4: Remove the dust cover of the optical module;

Step 5: Insert the jumper into the optical module interface;

Step 6: Repeat the above steps for the optical module at the other end of the link; Step 7: Check the status of the port LED.

conclusion

When the inserted optical module fails to function properly, it may be caused by a malfunction of the optical components or improper operation during installation. We should understand the basic information about troubleshooting and testing procedures for optical modules, and take corresponding methods to solve these optical module faults.